/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */

/*
 * This package is based on the work done by Timothy Gerard Endres
 * (time@ice.com) to whom the Ant project is very grateful for his great code.
 */

package org.apache.tools.tar;

/**
 * This class provides static utility methods to work with byte streams.
 * 
 */
// CheckStyle:HideUtilityClassConstructorCheck OFF (bc)
public class TarUtils {

  private static final int BYTE_MASK = 255;

  /**
   * Parse an octal string from a header buffer. This is used for the file permission mode value.
   * 
   * @param header
   *          The header buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The long value of the octal string.
   */
  public static long parseOctal(final byte[] header, final int offset, final int length) {
    long result = 0;
    boolean stillPadding = true;
    final int end = offset + length;

    for (int i = offset; i < end; ++i) {
      if (header[i] == 0) {
        break;
      }

      if ((header[i] == (byte) ' ') || (header[i] == '0')) {
        if (stillPadding) {
          continue;
        }

        if (header[i] == (byte) ' ') {
          break;
        }
      }

      stillPadding = false;
      // CheckStyle:MagicNumber OFF
      result = (result << 3) + (header[i] - '0');
      // CheckStyle:MagicNumber ON
    }

    return result;
  }

  /**
   * Parse an entry name from a header buffer.
   * 
   * @param header
   *          The header buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The header's entry name.
   */
  public static StringBuffer parseName(final byte[] header, final int offset, final int length) {
    final StringBuffer result = new StringBuffer(length);
    final int end = offset + length;

    for (int i = offset; i < end; ++i) {
      if (header[i] == 0) {
        break;
      }

      result.append((char) header[i]);
    }

    return result;
  }

  /**
   * Determine the number of bytes in an entry name.
   * 
   * @param name
   *          The header name from which to parse.
   * @param buf
   *          The buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The number of bytes in a header's entry name.
   */
  public static int getNameBytes(final StringBuffer name, final byte[] buf, final int offset, final int length) {
    int i;

    for (i = 0; (i < length) && (i < name.length()); ++i) {
      buf[offset + i] = (byte) name.charAt(i);
    }

    for (; i < length; ++i) {
      buf[offset + i] = 0;
    }

    return offset + length;
  }

  /**
   * Parse an octal integer from a header buffer.
   * 
   * @param value
   *          The header value
   * @param buf
   *          The buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The integer value of the octal bytes.
   */
  public static int getOctalBytes(final long value, final byte[] buf, final int offset, final int length) {
    int idx = length - 1;

    buf[offset + idx] = 0;
    --idx;
    buf[offset + idx] = (byte) ' ';
    --idx;

    if (value == 0) {
      buf[offset + idx] = (byte) '0';
      --idx;
    } else {
      for (long val = value; (idx >= 0) && (val > 0); --idx) {
        // CheckStyle:MagicNumber OFF
        buf[offset + idx] = (byte) ((byte) '0' + (byte) (val & 7));
        val = val >> 3;
        // CheckStyle:MagicNumber ON
      }
    }

    for (; idx >= 0; --idx) {
      buf[offset + idx] = (byte) ' ';
    }

    return offset + length;
  }

  /**
   * Parse an octal long integer from a header buffer.
   * 
   * @param value
   *          The header value
   * @param buf
   *          The buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The long value of the octal bytes.
   */
  public static int getLongOctalBytes(final long value, final byte[] buf, final int offset, final int length) {
    final byte[] temp = new byte[length + 1];

    TarUtils.getOctalBytes(value, temp, 0, length + 1);
    System.arraycopy(temp, 0, buf, offset, length);

    return offset + length;
  }

  /**
   * Parse the checksum octal integer from a header buffer.
   * 
   * @param value
   *          The header value
   * @param buf
   *          The buffer from which to parse.
   * @param offset
   *          The offset into the buffer from which to parse.
   * @param length
   *          The number of header bytes to parse.
   * @return The integer value of the entry's checksum.
   */
  public static int getCheckSumOctalBytes(final long value, final byte[] buf, final int offset, final int length) {
    TarUtils.getOctalBytes(value, buf, offset, length);

    buf[(offset + length) - 1] = (byte) ' ';
    buf[(offset + length) - 2] = 0;

    return offset + length;
  }

  /**
   * Compute the checksum of a tar entry header.
   * 
   * @param buf
   *          The tar entry's header buffer.
   * @return The computed checksum.
   */
  public static long computeCheckSum(final byte[] buf) {
    long sum = 0;

    for (int i = 0; i < buf.length; ++i) {
      sum += TarUtils.BYTE_MASK & buf[i];
    }

    return sum;
  }
}
